The Internet has enabled the delivery of electronic content to billions of people. Some content providers desire to send additional content items to users who visit a website hosted by a third-party publisher system. To do so, content providers may rely on a content delivery service that delivers the additional content items to computing devices of such users. In one approach, a content provider provides, to the content delivery service, data that indicates one or more user attributes that users must satisfy in order to receive the additional content items. The content delivery service creates a content delivery campaign that includes the data and is intended for sending additional content items to computing devices of users who will visit the website. However, if too many content items of a particular type are displayed at one time, then users that are not interested in content items of that type will begin to ignore those content items completely and will be less likely to interact with those content items.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.